Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.67   11.693%   $59.9456   $59.95   $59.95   $59.90  
  Purchase #2 $62.53   6.713%   $66.7276   $66.73   $66.75   $66.70  
  Purchase #3 $56.33   9.119%   $61.4667   $61.47   $61.45   $61.50  
  Purchase #4 $195.43   3.103%   $201.4942   $201.49   $201.50   $201.50  
  Purchase #5 $80.26   12.319%   $90.1472   $90.15   $90.15   $90.10  
  Purchase #6 $117.69   3.836%   $122.2046   $122.20   $122.20   $122.20  
  Purchase #7 $113.31   6.822%   $121.04   $121.04   $121.05   $121.00  
  7 purchase totals = $679.22       $723.0259   $723.03   $723.05   $722.90